In travel, as in life, there are heroes and villains. There’s good and evil. And there’s Southwest Airlines and Spirit Airlines.

Both are no-frills discount carriers, and both are success stories in the economic sense. But that’s where the similarities end.

Spirit is known for its preponderance of fees, the risqué tone of some of its ads (as in the naughty “MILF” acronym for its “Many Islands, Low Fares” sale), and a take-it-or-leave-it attitude toward customer service. Southwest has a reputation for inclusive fares (one of the few airlines left that don’t charge extra for a checked bag), a Texas-style hospitality (concerts on planes), and its famous customer-focused way.

A look at these airlines offers a window into the relationship between air carriers and their customers, revealing why the modern flying experience can be so infuriating.

For Southwest—the Dallas carrier founded in 1971—customer service is part of its corporate DNA. Consider what happened to Robert Siegel. The retired engineer and his wife, Ruth, were scheduled to fly from West Palm Beach to Philadelphia when Ruth was diagnosed with lung cancer; her doctor ordered her to cancel the trip. Even though the tickets were nonrefundable, Siegel requested an exception. “Within one week, a complete credit had been posted to my credit card,” he says.

Southwest routinely waives its requirements in the interests of “Customer Service.” (It also has an annoying habit of uppercasing key words, like “People.”) Several years ago, one of its pilots even held the plane for a passenger so that he could make his grandson’s funeral. It doesn’t punish customers with ticket change fees or price its less restricted tickets so that only business travelers on an expense account can afford them. It’s not perfect, of course. Southwest’s prices can sometimes be significantly higher than the competition’s. And its one-class service is too egalitarian for many business travelers.

Spirit Airlines styles itself as the anti-Southwest. The airline, based in the suburbs of Fort Lauderdale, has its roots in the trucking business, which may explain a lot: Its customers often complain that they are treated like cargo. Seems Spirit wouldn’t have it any other way.

Spirit often does the exact opposite of what Southwest would. When Vietnam vet Jerry Meekins was told his esophageal cancer was terminal and advised by his doctor to cancel his flight from Florida to Atlantic City, the airline refused a refund request. Only after veterans groups intervened did the carrier cave, and only reluctantly. In an effort to not set a precedent, CEO Ben Baldanza said he personally would pay for the refund, not his airline.

And Spirit does love fees. Fully one-third of its ticket revenue comes from fees (compared with 7.5 percent for Southwest). Spirit argues that its passengers just crave low fares, and that all of the extras are optional. But some passengers complain that the fees aren’t adequately disclosed and that some are ridiculous (a $100 charge to carry—that’s right, carry—a bag on a plane if you didn’t prepay a lower fee online). Where Southwest’s employees have a reputation for being sociable, Spirit’s can be on the surly side. Baldanza once inadvertently replied directly by e-mail to a passenger this way: “Let him tell the world how bad we are. He’s never flown us before anyway and will be back when we save him a penny.”

Baldanza has a point, and it’s one that drives consumers (and consumer advocates) crazy: If you can navigate the maze of fees, restrictions, and Spirit’s $9 Fare Club ($60 per year, with automatic reenrollment whether you fly or not), you can travel for impressively low fares. And stockholders love their shares of SAVE (Spirit’s ticker symbol) about as much as they do Southwest’s (aptly, LUV).

I’d say Spirit enjoys playing the villain as much as Southwest likes being the hero. Spirit certainly hasn’t suffered for it financially. These two airlines represent one of travel’s most enduring paradoxes: that companies offering poor customer service can succeed as well as those offering good customer service. Spirit’s success defies an easy explanation, unless you have a degree in psychology. Spirit taps into the very human need to snag a deal. But understanding what makes us tick and the way we can be manipulated points to a better future for every traveler. See, Southwest and Spirit are not the only examples of travel’s curious yin and yang. Whether you’re staying at a hotel, renting a car, or taking a cruise, you’ve faced the same kinds of choices between companies. At the beginning of 2013, many of these companies find themselves at a crossroads, wondering which path to take: the embrace of a LUV or the thriftiness of a SAVE. Both clearly work in the short term. But Southwest operates on the principle that, eventually, customers will catch on.

Then again, maybe not. If people continue to fall for the ultralow, lots-of-strings-attached rates, then the treatment of passengers like cargo might continue indefinitely. Travelers must consider more than the price when they book their ticket or make arrangements to take a cruise or rent a car. They have to take a company’s service reputation into account, too. Reward the heroes of the travel industry with your business. Otherwise, the villains win.